Holocene environmental change in Rotsee and its impact on sedimentary carbon storage

Cindy De Jonge, Nathalie Dubois, Nemiah Ladd, Longhui Deng, Niroshan Gajendra, Negar Haghipour, Carsten Schubert, Mark Lever

To assess the long-term impact of climate change and human influence on lakes and their sedimentary carbon storage, paleo-environmental approaches using well-dated lake sediment cores can be employed. Here, we reconstruct carbon mass accumulation rates for organic and inorganic carbon since 13 ka BP in Rotsee, a perialpine lake near the Swiss Alps, using a 12m sediment core. A multiproxy approach (XRF, carbon and nitrogen isotopes, organic macromolecule chemical compositions, aDNA) was used to explore changes in the lake system that affect sedimentary carbon storage. The Early Holocene (11.8 to 7 cal ka BP) was characterized by a mixed phytoplankton and watershed-derived provenance of organic matter, and the deposition of inorganic and organic sedimentary carbon. Warming during the Holocene Thermal Maximum (9.8 to 8.8 cal ka BP) increased sedimentary carbon storage. In the Mid- to Late Holocene (7 to 1 cal ka BP), the sedimentary record indicates an increased influx of allochthonous, vascular plant-derived organic matter, and low production or conservation of phytoplankton-derived carbon. Organic carbon storage increased, while inorganic carbon became negligible. Larger deforestation events, potentially during Neolithic times (around 4 ka BP), but especially during Roman times (2 ka BP), coincided with further increased organic carbon MARs. Recent sediments, influenced by eutrophication in the last century, show higher carbon accumulation rates compared to earlier Holocene periods. Rotsee serves as a case study of how climate warming and human land use changes have influenced lake development and sedimentary carbon storage, with broader implications for understanding carbon dynamics in high altitude lakes and their future carbon balance.